1. Technical Field
The present invention relates to a structure for mounting a compound circuit to a circuit board, the compound circuit including a high voltage circuit and a low voltage circuit whose supply voltages are different from each other.
2. Background Art
In a case where a compound circuit including a high voltage circuit and a low voltage circuit whose supply voltages are different from each other is mounted on circuit board, it has heretofore been proposed to mount the high voltage circuit and the low voltage circuit on separate circuit boards and to arrange the circuit boards by stacking them as layers, for the purpose of suppressing the increase of the arrangement area (refer to, for example, JP-A-2005-257865 and JP-A-2006-9687).
As an example of the field in which the compound circuit including the high voltage circuit and the low voltage circuit is used as stated above, there is mentioned an electric vehicle (EV) or a hybrid vehicle (HEV being a vehicle which conjointly uses an engine and a motor-generator). In such a vehicle, the low voltage circuit which operates with the same voltage (for example, an effective voltage of 12 V) as that of a conventional vehicle employing the engine as a power source is disposed in relation to a control system and electric accessories within the vehicle. Besides, the high voltage circuit which operates with a voltage (for example, an effective voltage of 200 V) higher than that of the low voltage circuit is disposed in relation to a motor (or the motor-generator) being a power source and the peripheral equipment thereof.
In the compound circuit of the electric vehicle or the hybrid vehicle as stated above, a countermeasure for preventing any abnormal discharge due to shorting becomes especially important in the designs of the circuit and the circuit board. This is ascribable to the fact that a battery which is installed on the vehicle shifts from a lead storage battery to a lithium ion battery of higher voltage. More specifically, in the lithium ion battery, the damage of a battery function attributed to the abnormal discharge is heavier than in the lead storage battery, and the heat generations of the lithium ion battery itself and the wiring lines thereof during the abnormal discharge are more than in the case of the lead storage battery.
Besides, even in fields other than the vehicles, in the designs of the circuit and the circuit board, attention needs to be paid to the prevention of shorting in the case where the compound circuit including the high voltage circuit and the low voltage circuit is mounted on the circuit board, more than in a case where the low voltage circuit is singly mounted on the circuit board. This is important irrespective of whether or not the lithium ion battery suffering from the serious damage during the shorting is employed as a power source. Especially in the field of a commodity which is used in an environment liable to dew condensation, the prevention of the occurrence of shorting due to a waterdrop ascribable to the dew condensation must be sufficiently cared about.
In this regard, the background-art documents mentioned above, merely suggest a measure in design as suppresses the arrangement area of the circuit board, and they indicate nothing about a countermeasure against the shorting as stated above.